optimization - Why padding is used in Base64 encoding? -


possible duplicate:
why base64 encoding requires padding if input length not divisible 3?

quoting wikipedia:

...these padding characters must discarded when decoding still allow calculation of effective length of unencoded text, when input binary length not multiple of 3 bytes. ...

but calculation of length raw data can done if strip padding character.

          |               encoded           |-------------------------------------- raw size  | total size | real size | padding size 1         | 4          | 2         | 2 2         | 4          | 3         | 1 3         | 4          | 4         | 0 4         | 8          | 6         | 2 5         | 8          | 7         | 1 6         | 8          | 8         | 0 7         | 12         | 10        | 2 8         | 12         | 11        | 1 9         | 12         | 12        | 0 10        | 16         | 14        | 2 . . .

so given real encoded size (third column) can correctly guess padded size be:

paddedsize = 4 * ceil (realsize / 4)

so in theory, there no need of padding. algorithm have handled it. considering base64 encoding popular industry standard, used in many applications , devices. these have benefited reduced encoded size. question is, why padding used in base64 encoding?

it makes encoded message integer multiple of 4 characters. might make writing decoder easier. can load , process characters in blocks of 4 , convert them 3 output characters, , padding makes easy without going off end of string.


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